Sound recording apparatus



July 23, 1940. G. L.. DIMMICK SOUND RECORDING APPARATUS Filed March 3l, 1959 2 Sheets-Sheet` l Pil G. Z., }FEVUMEHF OPIQUE jl wwvf:

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SOUND RECORDING APPARATUS Filed March 31, 1959 2 sheets-sheer 2 PEA/UNER@ wo rural? TIM/NG c/ncu/'r G. Gib.,

a Snucntor Glenn, Le zammz'ci Cttornej Patented July 23, 1940 PATENT OFFICE SOUND RECORDING APPARATUS Glenn L. Dimmick, Haddonfield, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application March 31, 1939, Serial No. 265,279

5 Claims.

This invention relates to sound recording apparatus and more particularlyto apparatus for recording sound on lm by what `is known as the penumbra `type of variable density4 system.

The subjectmatter of,` this application is an improvement on the apparatus described and claimed in my Patent No. 2,095,3l7,issued October 12, 1937. In the said patent, apparatus is described and claimed for making avariable den-` sity sound recordby the penumbra method` and the present apparatus distinguishes thereover in that the apparatus is so modified that either volume compression or variation in the slope of the Variable density curve, or both, may be produced.

In the performance of my invention, I take advantage of the fact that the intensity gradient of the penumbra depends upon the distance of the penumbra mask from .the filament or :lilament image. When themask is located close to the iilament the intensity Ivaries gradually, whereas as the mask approaches the area on which the penumbra is to be projected the gradient becomes quite steep. By moving the penumbra mask back and forth in` accordance with the sound volume, I am able to vary the intensity gradient as desired and to thereby change the variation in light intensity for given galvanometer deiiection, as desired, and I take advantage of this fact to produce volume compression or change in slope of the variable `density curve as may be` required. f i

One object of the invention is to provide an improved method of `and apparatus for variable density recording.

Another object ofthe invention is to provide v an improved apparatus `for volume compression.

Another object of the invention is to provide an improved type of variable density sound track.

Another object of the invention is vto provide a penumbra type of recording apparatus" with a movable penumbra mask.

Another object of the invention is to provide an improved type of squeeze track recording.

Another objectof thefinvention is to provide an improved penumbra mask.

Other andincidental objectsof the invention will be apparent to those skilledA in the art from a reading of the following speciiication and an inspection of the accompanying drawings,` in which f Figure 1 is a diagrammatic illustration of a penumbra recorder with the penumbra mask in one position;

Figure `2 is an illustration .corresponding to light intensity of the shift in penumbra mask position; :5.

Figure 4 illustrates a modied form of apparatus using two penumbra masks;

Figure 5 is a curve of galvanometer deection plotted against slit illumination for the apparatus shown in Fig. 4; v 10 Figure 6 isa diagrammatic illustration of` an apparatus for shifting the penumbra mask along the axis of the optical system in accordance with thevolume of the sound recorded to produce volume compression; 15

Figure 7 is a diagrammatic illustration of an apparatus `for shifting the penumbra mask along the optical axis of the recording optical system and simultaneously perpendicular to the said axis in order to produce both volume compression and ground noise reduction;

Figure 8 illustrates a modified form of apparatus for accomplishing either volume compression, ground noise reduction, or both, as desired;

Figure 9 is a curve showing slit illumination plotted against galvanometer deflection for the apparatus shown in Fig. 8;

Figure 10a is a View of a penumbra mask of the customary `type from one end of the optical system; I i

Figure 10b is a view, corresponding to 10a, of an improved form of penumbra mask; Figure 11 is a curve showing galvanometer deflection plotted against slit illumination for vthe form of penumbra mask shown in Fig. 10b; and

Figure 12 shows an apparatus similar to that of Fig. 6 combined with a double Vane shutter in order to produce a squeeze track recording combined with volume compression.

Referring first to Fig. 1, this figure shows the portion of a recording optical system from the o lamp toward the galvanometer in an apparatus such as shown in my patent above referred to. The lamp lament is indicated at l0 and, `as shown, is of appreciable diameter since an electrical filament is used. The opaquepenumbra 5 vane is shown vat Il reaching tothe optical axis of the system. The penumbra is indicated-as lying in the plane I2, which plane is usually the plane of the recording slit in an optical system. The height of the penumbra is indicated by the bracket and rangesfrom a maximum of intensity at the top to substantially zero intensity at the bottom.

. In Fig. 2 the penumbra mask or vane `H is 5 penumbra shown in Fig. l but this range covers a shorter distance. If the light from the arrangement shown 'in Figs. l and 2 is directed to a galvanometer mirror and from the galvanometer mirror through a slit to the film, as illustrated in the aforesaid patent, or in Fig. 12 of the present application, then the variation in light intensity for a given galvanometer deiiection is as indicated in Fig. 3. If the normal galvanometer position in relation to the slit be considered as i'ifty per cent illumination,rthen the penumbra shown in Fig.,l will have the slope indicated in the solid line when galvanometer deection is plotted against siit illumination and it will be apparent that this slope is rather gradual. On the other hand if the penumbra mask or vane is moved to the position shown in Fig. 2, the relatively shorter penumbra will provide the much steeper slope shown in the dashed line and a correspondingly greater change in illumination will be produced in proportion to the galvanometer deflection.

One way to take advantage of this eiect is shown in Fig. 4. In this case a pair of penumbra masks I3 and I4 are provided which are spaced along the optical axis. Itrwill be apparent that light from the filament II) passing the mask I3 will produce the upper half of the .penumbra in the image plane I2 which will be spread out in the same manner as isthe pneumbra in Fig. 1. On the other hand the'light from the upper portion of the filament passing the second mask I4 will produce the lower half of the penumbra in the image plane I2 which will be correspondingly shorter or compressed, as is the case in Fig. 2. If the light beam after passing these penumbra masks is deflected by a galvanometer mirror in the customary manner, then the galvanometer deflection as plotted against slit illumination will appear as shown in Fig. 5, where the lower portion of the curve indicates the relatively steep slope of the lower portion of the penumbra in Fig. 4, while the upper portion of the curve indicates the more gradual slope of the upper portion of the penumbra shown in Fig. 4. It will be apparent that the use of these two fixed penumbra masks accordingly produces a type of volume compression in accordance with the curve of Fig. 5.

In the form of the invention shown in Fig. 6 the penumbra vane II is connected to a movable member of the motor I5 which in turn is connected to an appropriate rectifier, filter and timing circuit I6. This rectifier, filter and timing circuit arrangement may be a conventional groundnoise reduction amplier, such as shown and, described, for example, in McDowell Patent 1,856,197, or in Kreuzer Patent 1,999,700. When the envelope of the sound waves changes, the motor I5 which may, as illustrated, consist merely of a solenoid with a movable iron plunger., is actuated toshift the penumbra mask II along the optical axis of the system. The effect of movement of this vane dependson the direction of connection of the apparatus. If increased sound volume causes the vane to move toward the left to increase the height of the penumbra, then compression of the volume ran-ge is obtained. If the apparatus is so connected that increased sound volume causes the vane Il to move to the right and to thereby decrease the height of the penumbra in the plane I2 to the smaller dimension indicated by the lines I1, then volume expansion results, the penumbra position when the vane II is in the left hand position being indicated by the lines I8. v

In the apparatus shown in Fig. 7, the penumbra mask II is arranged to rotate about the pivot I9 while the motor I5 is connected as shown in Fig. 6 to swing the penumbra mask about that pivot. A second fixed penumbra vane 20 is provided as described and claimed in the joint application of J. L. Underhill and myself, Serial No.. 210,592, led May 28, 1938, RCV Docket 6032. In this arrangement movement of the penumbra vane Il about the pivot I9 in accordance with the envelope of the sound waves accomplishes both ground noise reduction as described and claimed in the said application due to the vertical component Aof motion, or motion perpendicular to the optical axis, and the movement of the vane along the optical axis accomplishes volume compression simultaneously. If the rotary motion indicated in Fig. 7 is not desired, then the motor illustrated in Fig. 6 may be bodily substituted for that shown in Fig. 7 and set at an angle with the optical axis so that the vane II will move along a fixed axis intersecting the optical axis and producing the same effect as shown in Fig. 7. The fixed vane 20 is so placed that it forms an optical end Astop for the penumbra. The vane I I is so adjusted that it may move past the end of the vane 20 but any such further movement does not affectthe penumbra. This arrangement permits the use of an amplifier in which the current operating the motor I5 varies in direct instead of inverse proportion to the envelope of the sound waves.

In the above described forms of the invention, the penumbra has been produced by a vane of opaque material. The same result may be accomplished las shown in Fig. 8 by a plate of opaque material having a convex curve upon its surface as the portion of the surface to which the Yrays are tangent is the only part affecting l plate the light intensity distribution of the pe- ,Q

numbra may be varied as desired. For example, the plate shown in Fig. 8 will produce a curve of galvanometer deflection plotted against slit illumination substantially as shown in Fig. 9

and this curve may be varied as desired by varying the curvature. By moving the plate in Fig. 8 up and down in accordance with the sound envelope both volume compression and noise reduction may be secured. The relation between the quantities of volume compression and noise reduction may be controlled by choosing or shifting the location of the pivot 2I about which the curve plate 22 is rotated. In order vto avoid stray light effects and similar undesirable reflecting effects, the upper surface of the movable plate 22 should be appropriately rendered non-reflecting. For example, the surface may be sandblasted and finished in black or it may be provided with transverse grooves to provide a substantially continuous series of diaphragm edges or narrow diaphragms may be secured thereto closely adjacent to each of them.

The active edge of the penumbra vanes and masks above described and heretofore used has been straight when they lay at right angles to the optic axis and when they were Viewed along the optic axis, as, for example, from the position of the light filament, this arrangement being shown in Fig. 10a. The edge of the penumbra mask, however, may be provided with saw teeth of triangular or other shape, as shown in Fig. 10b. This saw tooth arrangement will produce a penumbra having an intensity distribution substantially as shown in Fig. 11. In this figure the dashed lines indicate the intensity distribution, in terms oi galvanometer deflection, plotted against slit illumination for a penumbra mask having a straight edge, while the solid line indicates the corresponding functions of a penumbra mask having a saw tooth edge, such as shown in Fig. 10b. It will be apparent that a more or less S-shape curve results. This shape of curve is sometimes desired in order to make overloading of the sound track less noticeable and correspondingly less objectionable. This effect may be produced likewise in the penumbra mask of Fig. 8 by providing longitudinal V-shaped grooves on the plate 22.

Instead of the saw tooth edge shown in Fig. 10b I may provide the penumbra mask of 10a with a translucent edge or with an edge of graded translucence in order to accomplish the same result as is accomplished by the saw tooth edge. Alternatively, I may make the entire penumbra mask partly transparent or translucent to give a diffused illumination and the edge of this mask may, in turn, have a graded light translucence.

For a constant amplitude of galvanometer vi bration and a constant brightness of light source, the volume of sound obtained from a penumbra type variable density record is inversely proportional to the height of the penumbra and directly proportional to the length of the recording light beam which determines the Width of the sound track. If a shutter controlling the length of the light beam and therefore the width of the sound track is mechanically or electrically coupled to the penumbra vane in such `a manner that the height of the penumbra is directly proportional to the length of the recording beam, then the sound volume obtained from the track would be proportional to the original volume but the surface noise due to dirt, scratches and film grain would decrease with decreasing sound volume. Such an automatic squeeze track recording system is illustrated in Fig. 12 which shows the portion of a recording optical system from the lamp to the galvanometer mirror. In this arrangement a double vane shutter may be used, such, for example, as described and claimed in Hasbrouck Patent 2,102,778 or Baker Patent 2,102,776. In this arrangement the penumbra vane is connected to the shutter actuating motor so that the shutter vanes and penumbra vane are simultaneously actuated. It will be apparent that the shutter motor and the penumbra motor may be independent, as, for example, by using a penumbra vane motor, such as illustrated in Fig. 6 or Fig. 7, connected to the output oi the same amplifier as a shutter motor such as shown in the patents just referred to.

Having now described my invention, I claim:

1. In a recording optical system of the penumbra type, a penumbra mask consisting of a plate of opaque material convexly curved toward the optical axis of the optical system.

2. In a recording optical system of the penumbra type, a penumbra mask consisting of a plate of opaque material convexly curved toward the optical axis of the optical system, and means for moving the said mask toward and away from the optical axis in accordance with the envelope oi the sound waves to be recorded.

3. A penumbra mask for use in a sound recording optical system, consisting of a body of opaque material having serrations therein along the edge defining the penumbra.

4. A penumbra mask for use in a sound record- GLENN L. DIMMICK. 

